1. Field of Invention
The present invention relates to a method for forming a circuit by use of an electrically conductive paste for forming a printed circuit on a baseboard.
2. Related Art
As one of methods for producing printed circuit boards, an electrically conductive paste is coated on an insulating base board in accordance with a predetermined circuit pattern, and is heated or dried to be hardened, said electrically conductive paste comprising electrically conductive fillers such as metallic powder, metallic short fiber or carbon black dispersed in a thermoplastic resin or a thermosetting resin.
However, in this method, in case the content of the electrically conductive fillers is increased for heightening electrical conductivity, the content of the resin is relatively decreased and the adhesive strength between the electrically conductive paste and the insulating base board is lowered to easily cause the circuit to separate from the insulating base board. Further, a coating property of the paste when forming the circuit pattern or maintenance of the shape of the circuit pattern will be worsened.
Further, as to the content of the electrically conductive fillers, a unique electric characteristic is generally known that the content thereof up to about 600 to 700 phr in relation to the resin will decrease the electric resistance rate, but 800 phr or more will reversely increase the electric resistance rate. The content of the fillers is limited for increasing the electric conductivity.
The invention has been made in consideration of such situations. It is accordingly an object of the invention to provide a method for forming a circuit which is excellent in the coating property of the electrically conductive paste when forming a circuit pattern or maintenance of the shape of the circuit pattern as well as excellent in the electric conductivity and the adhesive strength with a base board.
For attaining the object, the method of the invention for forming a circuit is characterized in that a circuit pattern is formed with an electrically conductive paste (sometimes called briefly as xe2x80x9cpastexe2x80x9d hereafter) composed by mixing, in a resin, electrically conductive fillers (sometimes called briefly as xe2x80x9cfillerxe2x80x9d or xe2x80x9cfillersxe2x80x9d hereafter) whose shapes have aspect ratios and a magnetic material whose shape has an aspect ratio, and said circuit pattern is hardened while a magnetic line of force is being exerting in the thickness direction of said circuit pattern. Further, for attaining the same object, the method for forming a circuit is characterized in that a circuit pattern is formed with the paste composed by mixing, in a resin, complexes of fillers whose shapes have aspect ratios and a magnetic material, and said circuit pattern is hardened while a magnetic line of force is being exerting in the thickness direction of said circuit pattern.